During a navigated surgical procedure a surgeon typically needs to correlate the position of previously acquired patient imaging (such as MRI), with the physical position of the patient who is to be operated on. This is typically achieved by employing a surgical navigation system that integrates both the patient imaging and the patients positioning into a common coordinate space. Navigated surgical procedures also generally employ surgical instruments that are also integrated within this common coordinate space. This common coordinate space is formed by an amalgamation of the virtual coordinate space of the system used to perform registration and the actual coordinate spaces. Wherein the actual coordinate space is defined as the space where actual objects such as the patient and tools exist and the tracking coordinate space will be defined as the space wherein only physical objects visible to the tracking detector are locatable such as tracking markers. Correlation of the patient imaging with the physical position of the patient is accomplished through the process of registration to this common coordinate space. Ensuring that the correlation is accurate is desirable and necessary for maintaining surgeon confidence in the information being presented to them and in ensuring the navigated procedure is optimally executed.
However, presently it tends to be difficult to maintain accurate correlation of patient imaging and positioning as described by the paper [The Silent Loss of Navigation Accuracy; Research-Human-Clinical Studies; Vol. 72, No. 5, May 2013, pages 796-807]. Presently this accuracy is typically reported to a surgeon as a confidence or tolerance number at the time that registration is computed. This number is not indicative of the complexity of registration accuracy, and, more significantly, is not indicative of the fact that accuracy can vary in different parts of the surgical field and throughout the progression of the procedure. Further, this number is used as a one-time accept/reject criterion for the registration—once the registration is accepted typically it is assumed to be correct for the duration of the procedure, or until the surgeon notices that something is significantly misaligned.
With the present state of the art inaccuracy of the navigation system is difficult to identify as a typical system only presents a virtual representation of the OR procedure, and as such it cannot be readily contrasted to the actual physical state of the OR at a given time. Currently, for a surgeon to measure registration accuracy during a procedure he or she typically locates the tool relative to an identifiable location on the actual patient anatomy while noting the degree to which the location of the virtual tool is displaced from the same location relative to the virtualized patient anatomy, where such a virtual tool is displayed as an overlay on the three-dimensional imaging data from a scan of the patient's anatomy. Furthermore, once a registration misalignment is noticed, correcting for the error tends to be difficult, and often not achievable. Thus the embodiments provided in this disclosure attempt to alleviate some of the aforementioned shortfalls of presently employed surgical navigation systems.